The present invention relates to a liquid chromatograph mass spectrometer, and more particularly to a multidimensional liquid chromatograph mass spectrometer having a plurality of separation columns.
Liquid chromatograph mass spectrometers have been used to analyze sample solutions containing a plurality of components.
A liquid chromatograph mass spectrometer comprises: a liquid chromatograph which passes a sample through its separation column and thereby separates the components of the sample from one another by utilizing the fact that each component varies in its interaction with the column; and a mass spectrometer which ionizes the separated components one after another and detects the generated ions.
For analysis of a sample containing many species of components, a multidimensional liquid chromatograph mass spectrometer is used which includes a multidimensional liquid chromatograph having therein a plurality of separation columns connected in series to further separate the components from one another.
Examples of multidimensional liquid chromatograph mass spectrometers are described in Japanese Patent Laid-Open No. 3-175355 and Analytical Chemistry, 69 (1997), pp. 1518-1524.
Japanese Patent Laid-Open No. 62-255865 describes a liquid chromatograph which does not employ series-connected separation columns but in which a sample concentration column, a reaction column, and a separation column are connected in series.
The technique described in Japanese Patent Laid-Open No. 62-255865 supplies an eluent to a separation column while supplying a sample solution to a concentration column to concentrate it. When the concentration and the separation have been completed, the flow path switching valve is switched so as to supply a solution for desorption to the separation column through the concentration column and a reaction column.
The technique described in Japanese Patent Laid-Open No. 62-255865 allows the concentration and the separation to be carried out separately from each other, making it possible to select an optimum concentration method and optimum separation conditions.
Multidimensional liquid chromatograph mass spectrometers employ a plurality of columns using different separation principles.
The reason for this is that the first and second columns require different types of eluent for separation.
That is, when a cation exchange column is used as the first separation column, for example, an electrolyte solution having an appropriate concentration is used as the eluent. Electrolyte solution is not suitable as a solution introduced into a mass spectrometer.
Specifically, introducing an electrolyte solution into a mass spectrometer adversely affects it, such as reducing the ionization efficiency (and hence the detection sensitivity) and contaminating or clogging the ion sampling olifice. Therefore, electrolyte solution cannot be introduced into mass spectrometers.
This problem may be circumvented by using the technique described in Japanese Patent Laid-Open No. 62-255865, as follows. An electrolyte solution is supplied to the first separation column to separate a sample, which is then trapped in an appropriate trap column. After that, the flow path switching valve is switched so that the solution excluding the electrolyte solution, which can be introduced into the mass spectrometer, is supplied from the trap column to the second separation column so as to supply the separated sample to the mass spectrometer.
In this case, however, while the solution is being supplied from the trap column to the second separation column, that is, while the sample solution is being separated in the second separation column, the sample separation operation of the first column must be stopped. This means that the sample cannot be continuously supplied, and therefore the analysis takes a long time to complete.
Furthermore, in multidimensional liquid chromatograph mass spectrometers using a conventional technique, each of the plurality of separation columns takes a certain time to complete each separation operation. Therefore, the first column must stop its current separation operation until the second column connected in series to the first column completes its separation operation, making it impossible to continuously supply eluent from the first column to the second column.
Accordingly, in multidimensional liquid chromatograph mass spectrometers using a conventional technique, a fraction of eluted components including a target component(s) must be taken from the components eluted from the first separation column and introduced into the second column.
This means that even though these specific (selected) components can be measured, not all components contained in the sample solution can be measured.
To analyze all components contained in a sample solution, it is necessary to put the eluent from the first separation column into a plurality of sample loops or trap columns in fractions and sequentially introduce each fraction of eluent into the second separation column.
In this case, the time required for the second separation column to complete an entire separation operation is longer than when the eluent is not processed in fractions, since the time increases with the number of samples (fractions) taken from the eluent from the first separation column.
That is, the time it takes the entire analysis to complete is considerably long, as compared with ordinary liquid chromatograph mass spectrometers.
A biological sample must be analyzed in a short time. Therefore, the above method in which the eluent from the first separation column is processed in fractions cannot be used for biological samples.
Analysis requiring a long time to complete is not desirable even for samples other than biological samples.